Recent progress of digitization of various information, including image information and sound information, has caused rapid increase in the amount of digital information. In response to the situation, devices are being developed which can record information on optical discs which are suitable storage media for large-capacity, high-density storage.
Optical discs contain image information including, for example, image information taken privately and image information purchased on a network. The information is often valuable to the user. That makes important technology which prevents the information from missing. If the management information with which recording locations, etc. are managed for each piece of information contained in the optical disc is damaged, all information becomes unreadable. It is therefore especially important to prevent management information from missing and repair partially damaged management information.
Such a scheme is disclosed in Japanese Unexamined Patent Publication 7-249261/1995 (Tokukaihei 7-249261; published Sep. 26, 1995). The following will describe the management information repairing method of Tokukaihei 7-249261.
FIG. 8 is a conceptual diagram showing the structure of a conventional storage medium 11. The conventional storage medium has a plurality of information recording areas: a system information area 12, a primary management information area 13, a data area 14, and a secondary management information area 15. The areas 12 to 15 each contain a different type of information. The “information” here includes system information, primary management information, user information, and secondary management information.
The system information includes, for example, read/write conditions and is needed for a device which writes information on the storage medium to correctly perform various controls.
The user information is information recorded by users: for example, image information and program information.
The primary and secondary management information is information with which recording locations, etc. of each piece of the user information on the storage medium and defective areas of the storage medium are managed. Note that the primary management information typically has the same content as the secondary management information.
According to the conventional scheme, the primary management information is updated when user information is altered or added. The secondary management information is updated based on the primary management information if neither recording nor reading is done for a certain period of time or the main power supply for an information recording device is turned off.
When the main power supply for the information recording device is turned on, it is checked whether or not the primary management information can be normally read. If an reading error is detected, the primary management information is replaced with the secondary management information to restore the primary management information.
Recording the management information at two different locations in this manner makes it possible to restore the primary management information from the secondary management information even if the primary management information becomes unreadable.
However, if one of the sets of management information becomes unreadable due to a scratch, defect, etc., there remains only one set (either the primary or the secondary). That greatly reduces effects of preventing missing management information.
Tokukaihei 7-249261 suggests a solution to this problem. The document suggests to record the management information at three different locations and employ the individual sets of management information by decision of majority, to improve on the precision of the management information.